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• How do I collect SNMP readings from intermittently-connected sites?

  - by Luke404

  I am collecting SNMP data on-site for a number of systems, currently using Cacti. These systems are spread on a number of sites that aren't always connected to internet, but I also need to centralize the data on a single system (datacenter housed server) and get graphs out of it. If I directly poll remote systems with a centralized Cacti I'd loose data when a site is not connected to internet. I should record data on-site (I have a server at each site and I can run whatever I want on it) and then 'sync' everything to the central system. One hack could be a cacti or directly an rrdtool on site and then periodically rsync RRD data to the central Cacti system, but that doesn't sound like a 'clean' solution: every RRD would have to be defined at both places and rsync scripts setup with the specific file names. Can you suggest a better solution? Cacti is not a requirement but I'd like to use something like that on the central system. On-site systems need only to collect data I don't need to graph it there or manage users rights to view data and stuff like that, users will only access the centralized system.

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• Extremely high mysqld CPU usage with no active queries

  - by RadarNyan

  I have a VPS running Ubuntu 12.04 LTS with LEMP stack, followed the guide from Linode Library (since I'm using a Linode) to setup, and everything worked fine until now. I don't know what's wrong, but my CPU usage just goes up since a week ago. Today things getting really bad - I got 74% CPU usage so I went check and found that mysqld taking too much CPU usage (somewhere around 30% ~ 80%) So I did some Google Search, tried disable InnoDB, restart mysql, reset ntp / system clock (Isn't this bug supposed to happen more than a year ago?!) and reboot my VPS, nothing helped. Even with mysql processlist empty, I still get mysqld CPU usage very high. I don't know what I missed and have totally no idea, any advice would be appreciated. Thanks in advance. Update: I got these from running "strace mysqld" write(2, "InnoDB: Unable to lock ./ibdata1"..., 44) = 44 write(2, "InnoDB: Check that you do not al"..., 115) = 115 select(0, NULL, NULL, NULL, {1, 0}^[[A^[[A) = 0 (Timeout) fcntl64(3, F_SETLK64, {type=F_WRLCK, whence=SEEK_SET, start=0, len=0}, 0xbfa496f8) = -1 EAGAIN (Resource temporarily unavailable) hum... I did tried to disable InnoDB and it didn't fix this problem. Any idea? Update2: # ps -e | grep mysqld 13099 ? 00:00:20 mysqld then use "strace -p 13099", the following lines appears repeatedly: fcntl64(12, F_GETFL) = 0x2 (flags O_RDWR) fcntl64(12, F_SETFL, O_RDWR|O_NONBLOCK) = 0 accept(12, {sa_family=AF_FILE, NULL}, [2]) = 14 fcntl64(12, F_SETFL, O_RDWR) = 0 getsockname(14, {sa_family=AF_FILE, path="/var/run/mysqld/mysqld.sock"}, [30]) = 0 fcntl64(14, F_SETFL, O_RDONLY) = 0 fcntl64(14, F_GETFL) = 0x2 (flags O_RDWR) setsockopt(14, SOL_SOCKET, SO_RCVTIMEO, "\36\0\0\0\0\0\0\0", 8) = 0 setsockopt(14, SOL_SOCKET, SO_SNDTIMEO, "<\0\0\0\0\0\0\0", 8) = 0 fcntl64(14, F_SETFL, O_RDWR|O_NONBLOCK) = 0 setsockopt(14, SOL_IP, IP_TOS, [8], 4) = -1 EOPNOTSUPP (Operation not supported) futex(0xb786a584, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0xb786a580, {FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1 futex(0xb7869998, FUTEX_WAKE_PRIVATE, 1) = 1 poll([{fd=10, events=POLLIN}, {fd=12, events=POLLIN}], 2, -1) = 1 ([{fd=12, revents=POLLIN}]) er... now I totally don't get it x_x help

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• How do I replicate Gmail filtering (forwarding mostly)?

  - by projectdp

  I have reached the limits of Gmail forwarding. Before there was no need to verify forwarding addresses. It's a problem for me now because the addresses I want to forward to are not natural inboxes but automated systems with no way to track the verification email contents. I want to set this up for example: mobile - email - facebook-email - flickr-email - tumblr-email - posterous-email How do I do this without Gmail filters? I think I need to use fetchmail to watch my inbox and then autoforward to the above addresses. Is fetchmail the best solution to this issue? Any other MRA's? I'd like to do some more complicated things with the emails in an automated fashion too, how would I go about monitoring the inbox, doing some actions to the email before forwarding, and forward everywhere? prerequisites: a server: fetchmail daemon to poll the account local mailbox script to clean & forward appropriately (python probably) sendmail + ~/.forward file backup email account (Gmail probably) Any help would be greatly appreciated. I'm trying to automate my social content distribution.

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• Log connections to program

  - by Zac

  Besides for using iptables to log incoming connections.. Is there a way to log established inbound connections to a service that you don't have the source to (suppose the service doesn't log stuff like this on its own)? What I'm wanting to do is gather some information based on who's connecting to be able to tell things like what times of the day the service is being used the most, where in the world the main user base is, etc. I am aware I can use netstat and just hook it up to a cron script, but that might not be accurate, since the script could only run as frequently as a minute. Here is what I am thinking right now: Write a program that constantly polls netstat, looking for established connections that didn't appear in the previous poll. This idea seems like such a waste of cpu time though, since there may not be a new connection.. Write a wrapper program that accepts inbound connections on whatever port the service runs on, but then I wouldn't know how to pass that connection along to the real service. Edit: Just occurred to me that this question might be better for stackoverflow, though I am not certain. Sorry if this is the wrong place.

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• stopping fastcgi_cache for php-enabled custom error page

  - by Ian

  Since enabling the fastcgi_cache on my nginx server, my php-enabled custom error page has suddenly stopped working and I'm getting the internal 404 message instead. In nginx.conf: fastcgi_cache_path /var/lib/nginx/fastcgicache levels=1:2 keys_zone=MYCACHE:5m inactive=2h max_size=1g loader_files=1000 loader_threshold=2000; map $http_cookie $no_cache { default 0; ~SESS 1; } fastcgi_cache_key "$scheme$request_method$host$request_uri"; add_header X-My-Cache $upstream_cache_status; map $uri $no_cache_dirs { default 0; ~^/(?:phpMyAdmin|rather|poll|webmail|skewed|blogs|galleries|pixcache) 1; } the cache relevant stuff in my fastcgi.conf: fastcgi_cache MYCACHE; fastcgi_keep_conn on; fastcgi_cache_bypass $no_cache $no_cache_dirs; fastcgi_no_cache $no_cache $no_cache_dirs; fastcgi_cache_valid 200 301 5m; fastcgi_cache_valid 302 5m; fastcgi_cache_valid 404 1m; fastcgi_cache_use_stale error timeout invalid_header updating http_500; fastcgi_ignore_headers Cache-Control Expires; expires epoch; fastcgi_cache_lock on; If I disable the fastcgi_cache, the php-enabled 404 page works as it has for years. How would I disable the cache for the custom error page?

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• c# Named Pipe Asynchronous Peeking

  - by KJ Tsanaktsidis

  Hey all, I need to find a way to be notified when a System.IO.Pipe.NamedPipeServerStream opened in asynchronous mode has more data available for reading on it- a WaitHandle would be ideal. I cannot simply use BeginRead() to obtain such a handle because it's possible that i might be signaled by another thread which wants to write to the pipe- so I have to release the lock on the pipe and wait for the write to be complete, and NamedPipeServerStream doesnt have a CancelAsync method. I also tried calling BeginRead(), then calling the win32 function CancelIO on the pipe if the thread gets signaled, but I don't think this is an ideal solution because if CancelIO is called just as data is arriving and being processed, it will be dropped- I still wish to keep this data, but process it at a later time, after the write. I suspect the win32 function PeekNamedPipe might be useful but i'd like to avoid having to continuously poll for new data with it. In the likley event that the above text is a bit unclear, here's roughly what i'd like to be able to do... NamedPipeServerStream pipe; ManualResetEvent WriteFlag; //initialise pipe lock (pipe) { //I wish this method existed WaitHandle NewDataHandle = pipe.GetDataAvailableWaithandle(); Waithandle[] BreakConditions = new Waithandle[2]; BreakConditions[0] = NewDataHandle; BreakConditions[1] = WriteFlag; int breakcode = WaitHandle.WaitAny(BreakConditions); switch (breakcode) { case 0: //do a read on the pipe break; case 1: //break so that we release the lock on the pipe break; } }

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• Synchronize the position of two ScrollView views

  - by Billy

  I am trying to synchronize the positions of two ScrollViews. I'm trying to do this to display a tv guide listing. I have created a custom class that extends RelativeLayout to display the guide. This relative layout has four children: an imageview in the top left corner, a HorizontalScrollView to display the column headers in the top right, a ScrollView to display the row headers at the bottom left, and a ScrollView in the bottom right that contains the listings. This ScrollView then contains a HorizontalScrollView, which in turn contains a LinearLayout with multiple child views that display the data. I hope this explains it clearly, but here's a diagram to make it clearer: ____________ |__|___hsv___| | | | | | sv -> | | | hsv -> | |sv| ll -> | | | etc | | | | |__|_________| I set it up like this because I wanted the guide listings to scroll both horizontally and vertically, but there's no scroll view that does this. Also, I want the row and column headers to display no matter what position the guide listings are at, but I want them to be lined up properly. So I'm trying to find a way to synchronize the positions of the two hsv's, and to also synchronize the positions of the two sv's. I'm also trying to do it in a way that avoids just running a handler every few milliseconds to poll one view and call scrollTo on the other. I'm in no way sure that this is the best way to do it, but this is what I've come up with. If anybody has any other suggestions, please feel free!

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• How do I install LFE on Ubuntu Karmic?

  - by karlthorwald

  Erlang was already installed: $dpkg -l|grep erlang ii erlang 1:13.b.3-dfsg-2ubuntu2 Concurrent, real-time, distributed function ii erlang-appmon 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP application monitor ii erlang-asn1 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP modules for ASN.1 support ii erlang-base 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP virtual machine and base applica ii erlang-common-test 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP application for automated testin ii erlang-debugger 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP application for debugging and te ii erlang-dev 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP development libraries and header [... many more] Erlang seems to work: $ erl Erlang R13B03 (erts-5.7.4) [source] [64-bit] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false] Eshell V5.7.4 (abort with ^G) 1> I downloaded lfe from github and checked out 0.5.2: git clone http://github.com/rvirding/lfe.git cd lfe git checkout -b local0.5.2 e207eb2cad $ configure configure: command not found $ make mkdir -p ebin erlc -I include -o ebin -W0 -Ddebug +debug_info src/*.erl #erl -I -pa ebin -noshell -eval -noshell -run edoc file src/leex.erl -run init stop #erl -I -pa ebin -noshell -eval -noshell -run edoc_run application "'Leex'" '"."' '[no_packages]' #mv src/*.html doc/ Must be something stupid i missed :o $ sudo make install make: *** No rule to make target `install'. Stop. $ erl -noshell -noinput -s lfe_boot start {"init terminating in do_boot",{undef,[{lfe_boot,start,[]},{init,start_it,1},{init,start_em,1}]}} Crash dump was written to: erl_crash.dump init terminating in do_boot () Is there an example how I would create a hello world source file and compile and run it?

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• Client-Server Networking Between PHP Client and Java Server

  - by Muhammad Yasir

  Hi there, I have a university project which is already 99% completed. It consists of two parts-website (PHP) and desktop (Java). People have their accounts on the website and they wish to query different information regarding their accounts. They send an SMS which is received by desktop application which queries database of website (MySQL) and sends the reply accordingly. This part is working superbly. The problem is that some times website wishes to instruct the desktop application to send a specific SMS to a particular number. Apparently there seems no way other than putting all the load to the DB server... This is how I made it work. Website puts SMS jobs in a specific table. Java application polls this table again and again and if it finds a job, it executes it. Even this part is working correctly but unfortunately it is not acceptable by my university to poll the DB like this. :( The other approach I could think of is to use client-server one. I tried making Java server and its PHP client. So that whenever an SMS is to be sent, the website opens a socket connection to desktop application and sends two strings (cell # and SMS message). Unfortunately I am unable to do this. I was successfully to make a Java server which works fine when connected by a Java client, similarly my PHP client connects correctly to a PHP server, but when I try to cross them, they start hating each other... PHP shows no error but Java gives StreamCorruptedException when it tries to read header of input stream. Could someone please tell what I can try to make PHP client and Java server work together? Or if the said purpose can be achieved by another means, how? Regards, Yasir

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• JQuery BlockUI - How to unblock UI after file download?

  - by Dan

  Using ASP.Net, JQuery and BlockUI, I'm trying to unblock the UI after a download file dialog is shown. I block the UI when export button is clicked: <script type="text/javascript"> $(document).ready(function(){ $('#<%= BtnExport.ClientID%>').click(function(){ $.blockUI(); }); }); </script> After this, I generate the file server side using: private void SendFileToUser(byte[] file, string contentType, string filename) { Response.Clear(); Response.ContentType = contentType; Response.AppendHeader("Content-Disposition", "attachment; filename="+filename); Response.OutputStream.Write(file,0,file.Length); Response.OutputStream.Flush(); Response.End(); } After this code has executed, I would like to unblock the UI. I have considered different options: Poll using Ajax calls to see if the file has been generated. Store the file in Session and redirect to same page and generate download then. But both options seem ackward, and I think there must be a clever JavaScript way to get a handle on or wait for a file dialog. Any suggestions?

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• System.Web.Caching vs. Enterprise Library Caching Block

  - by ESV

  For a .NET component that will be used in both web applications and rich client applications, there seem to be two obvious options for caching: System.Web.Caching or the Ent. Lib. Caching Block. What do you use? Why? System.Web.Caching Is this safe to use outside of web apps? I've seen mixed information, but I think the answer is maybe-kind-of-not-really. a KB article warning against 1.0 and 1.1 non web app use The 2.0 page has a comment that indicates it's OK: http://msdn.microsoft.com/en-us/library/system.web.caching.cache(VS.80).aspx Scott Hanselman is creeped out by the notion The 3.5 page includes a warning against such use Rob Howard encouraged use outside of web apps I don't expect to use one of its highlights, SqlCacheDependency, but the addition of CacheItemUpdateCallback in .NET 3.5 seems like a Really Good Thing. Enterprise Library Caching Application Block other blocks are already in use so the dependency already exists cache persistence isn't necessary; regenerating the cache on restart is OK Some cache items should always be available, but be refreshed periodically. For these items, getting a callback after an item has been removed is not very convenient. It looks like a client will have to just sleep and poll until the cache item is repopulated. Memcached for Win32 + .NET client What are the pros and cons when you don't need a distributed cache?

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• The nexus of MSDeploy, MSBuild and Hudson

  - by roufamatic

  Hey, I have experience with MSBuild and Hudson, but am new to MSDeploy. I currently have a simple solution with one web application project. I set up a build configuration and am using the "Publish" command (Visual Studio 2010) to simply copy files to a local folder and do config file replacement. What I would like to do is automate this using Hudson. So I figure I'll create an MSBuild script that will Perform the build (by calling out to the project file with my desired build configuration) Call MSDeploy to do all the same things that the "Publish" command is doing, except copy the files to a different folder. Configure Hudson to poll subversion and perform steps 1 & 2 when changes are detected Step 2 is where I'm getting lost. I assumed that the project.xml file that was created by VS2010 corresponded to -verb:sync -source:manifest=project.xml options, but msdeploy is choking on that xml file so clearly that's not what it's intended for. What command is Visual Studio executing under the covers to perform the config file replacement and the file copy? How do I automate the Publish command?

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• best practice for directory polling

  - by Hieu Lam

  Hi all, I have to do batch processing to automate business process. I have to poll directory at regular interval to detect new files and do processing. While old files is being processed, new files can come in. For now, I use quartz scheduler and thread synchronization to ensure that only one thread can process files. Part of the code are: application-context.xml <bean id="methodInvokingJob" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean" <property name="targetObject" ref="documentProcessor" / <property name="targetMethod" value="processDocuments" / </bean DocumentProcessor ..... public void processDocuments() { LOG.info(Thread.currentThread().getName() + " attempt to run."); if (!processing) { synchronized (this) { try { processing = true; LOG.info(Thread.currentThread().getName() + " is processing"); List xmlDocuments = documentManager.getFileNamesFromFolder(incomingFolderPath); // loop over the files and processed unlock files. for (String xmlDocument : xmlDocuments) { processDocument(xmlDocument); } } finally { processing = false; } } } } For the current code, I have to prevent other thread to process files when one thread is processing. Is that a good idea ? or we support multi-threaded processing. In that case how can I know which files is being process and which files has just arrived ? Any idea is really appreciated.

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• How should I implement reverse AJAX in a Django application?

  - by Carson Myers

  How should I implement reverse AJAX when building a chat application in Django? I've looked at Django-Orbited, and from my understanding, this puts a comet server in front of the HTTP server. This seems fine if I'm just running the Django development server, but how does this work when I start running the application from mod_wsgi? How does having the orbited server handling every request scale? Is this the correct approach? I've looked at another approach (long polling) that seems like it would work, although I'm not sure what all would be involved. Would the client request a page that would live in its own thread, so as not to block the rest of the application? Would it even block? Wouldn't the script requested by the client have to continuously poll for information? Which of the approaches is more proper? Which is more portable, scalable, sane, etc? Are there other good approaches to this (aside from the client polling for messages) that I have overlooked?

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• Python with Wiimote using pywiiuse module

  - by Anon

  After seeing the abilities and hackibility of wiimotes I really want to use it in my 'Intro to programming' final. Everyone must make a python program and present it to the class. I want to make a game with pygame incorporating a wiimote. I found pywiiuse which is a very basic wrapper for the wiiuse library using c types. I can NOT get anything beyond LEDs and vibrating to work. Buttons, IR, motion sensing, nothing. I've tried different versions of wiiuse, pywiiuse, even python. I can't even get the examples that came with it to run. Here's the code I made as a simple test. I copied some of the example C++ code. from pywiiuse import * from time import sleep #Init wiimotes = wiiuse_init() #Find and start the wiimote found = wiiuse_find(wiimotes,1,5) #Make the variable wiimote to the first wiimote init() found wiimote = wiimotes.contents #Set Leds wiiuse_set_leds(wiimote,WIIMOTE_LED_1) #Rumble for 1 second wiiuse_rumble(wiimote,1) sleep(1) wiiuse_rumble(wiimote,0) #Turn motion sensing on(supposedly) wiiuse_motion_sensing(wiimote,1) while 1: #Poll the wiimotes to get the status like pitch or roll if(wiiuse_poll(wiimote,1)): print 'EVENT' And here's the output when I run it. wiiuse version 0.9 wiiuse api version 8 [INFO] Found wiimote [assigned wiimote id 1]. EVENT EVENT Traceback (most recent call last): File "C:\Documents and Settings\Nick\Desktop\wiimotetext.py", line 26, in <mod ule> if(wiiuse_poll(wiimote,1)): WindowsError: exception: access violation reading 0x00000004 It seems each time I run it, it prints out EVENT 2-5 times until the trace back. I have no clue what to do at this point, I've been trying for the past two days to get it working. Thanks!

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• python: nonblocking subprocess, check stdout

  - by Will Cavanagh

  Ok so the problem I'm trying to solve is this: I need to run a program with some flags set, check on its progress and report back to a server. So I need my script to avoid blocking while the program executes, but I also need to be able to read the output. Unfortunately, I don't think any of the methods available from Popen will read the output without blocking. I tried the following, which is a bit hack-y (are we allowed to read and write to the same file from two different objects?) import time import subprocess from subprocess import * with open("stdout.txt", "wb") as outf: with open("stderr.txt", "wb") as errf: command = ['Path\\To\\Program.exe', 'para', 'met', 'ers'] p = subprocess.Popen(command, stdout=outf, stderr=errf) isdone = False while not isdone : with open("stdout.txt", "rb") as readoutf: #this feels wrong for line in readoutf: print(line) print("waiting...\\r\\n") if(p.poll() != None) : done = True time.sleep(1) output = p.communicate()[0] print(output) Unfortunately, Popen doesn't seem to write to my file until after the command terminates. Does anyone know of a way to do this? I'm not dedicated to using python, but I do need to send POST requests to a server in the same script, so python seemed like an easier choice than, say, shell scripting. Thanks! Will

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• if (i == 2) or if (2 == i) ?

  - by Maroloccio

  I usually use if (i == 2) in preference to if (2 == i) On occasion, I would switch things around when writing xUnit-type tests from scratch so as to follow the assertion convention of "expected" preceding "actual". When adding to existing unit tests, I always follow the style I find. No matter what, I always try to keep things consistent. Today I checked out some code with a lot of "if (2 == i)" and started wondering: which style is more "popular" nowadays? is popularity language-dependent? The latter probably because I am aware of why the "if (2 == i)" became common in the first place (C heritage) and because I see some languages go as far as disallowing assignments within conditions (e.g. Python). I thought about downloading some sources: apt-get source linux-source eclipse openoffice.org expanding them and performing a quick grep: grep --color --include=*.java --include=*.c -ERI \ "if[[:space:]]*\([[:space:]]*[[:digit:]]+[[:space:]]==" . or creating a quick "poll": http://goo.gl/mod/ciMF after a bit of searching and asking around, I am still not sure. So I am asking you: which way to go?

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• Threads, Sockets, and Designing Low-Latency, High Concurrency Servers

  - by lazyconfabulator

  I've been thinking a lot lately about low-latency, high concurrency servers. Specifically, http servers. http servers (fast ones, anyway) can serve thousands of users simultaneously, with very little latency. So how do they do it? As near as I can tell, they all use events. Cherokee and Lighttpd use libevent. Nginx uses it's own event library performing much the same function of libevent, that is, picking a platform optimal strategy for polling events (like kqueue on *bsd, epoll on linux, /dev/poll on Solaris, etc). They all also seem to employ a strategy of multiprocess or multithread once the connection is made - using worker threads to handle the more cpu intensive tasks while another thread continues to listen and handle connections (via events). This is the extent of my understanding and ability to grok the thousand line sources of these applications. What I really want are finer details about how this all works. In examples of using events I've seen (and written) the events are handling both input and output. To this end, do the workers employ some sort of input/output queue to the event handling thread? Or are these worker threads handling their own input and output? I imagine a fixed amount of worker threads are spawned, and connections are lined up and served on demand, but how does the event thread feed these connections to the workers? I've read about FIFO queues and circular buffers, but I've yet to see any implementations to work from. Are there any? Do any use compare-and-swap instructions to avoid locking or is locking less detrimental to event polling than I think? Or have I misread the design entirely? Ultimately, I'd like to take enough away to improve some of my own event-driven network services. Bonus points to anyone providing solid implementation details (especially for stuff like low-latency queues) in C, as that's the language my network services are written in.

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• "Work stealing" vs. "Work shrugging"?

  - by John

  Why is it that I can find lots of information on "work stealing" and nothing on "work shrugging" as a dynamic load-balancing strategy? By "work-shrugging" I mean busy processors pushing excessive work towards less loaded neighbours rather than idle processors pulling work from busy neighbours ("work-stealing"). I think the general scalability should be the same for both strategies. However I believe that it is much more efficient for busy processors to wake idle processors if and when there is definitely work for them to do than having idle processors spinning or waking periodically to speculatively poll all neighbours for possible work. Anyway a quick google didn't show up anything under the heading of "Work Shrugging" or similar so any pointers to prior-art and the jargon for this strategy would be welcome. Clarification/Confession In more detail:- By "Work Shrugging" I actually envisage the work submitting processor (which may or may not be the target processor) being responsible for looking around the immediate locality of the preferred target processor (based on data/code locality) to decide if a near neighbour should be given the new work instead because they don't have as much work to do. I am talking about an atomic read of the immediate (typically 2 to 4) neighbours' estimated q length here. I do not think this is any more coupling than implied by the thieves polling & stealing from their neighbours - just much less often - or rather - only when it makes economic sense to do so. (I am assuming "lock-free, almost wait-free" queue structures in both strategies). Thanks.

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• Web-based game in Python + Django and client browser polling

  - by ty

  I am creating a text-based game that implements a basic model in which multiple (10+) players interact with data and one moderator watches them and sets certain environmental statistics that affect gameplay. Recently I have begun to familiarize myself with Django. It seems to me that it would be an excellent tool for creating a game quickly, particularly because the nature of my game depends largely on sets of data (which lends itself quite well to a database). I am wondering how to "push" changes made by the game moderator to the players (for example, the moderator can decide to display an image to all players). The game is turn-based, not real-time, but certain messages need to be pushed out in roughly real-time. My thoughts: I could have each player's browser poll a status periodically (say, every 30 seconds) to see if there is a message from a moderator. But this forces a lag and means different players might receive it at different times. And reducing this interval to <10 seems like a bad idea for the server. Is there a better way to inform clients of changes? Would you suggest something other than using a web framework like Django? Thanks!

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• Is there a java library / package analogous to <stdio.h>?

  - by Roboprog

  I have been doing Java on and off for about 14 years, and almost nothing else the last 6 years or so. I really hate the java.io package -- its legion of subclasses and adapters. I do like exceptions, rather than having to always poll "errno" and the like, but I could surely live without declared exceptions. Is there anything that functions like the Unix/ANSI stdio.h routines in C? I know we will never be rid of java.io and its conventions until java itself is retired, as they have metastasized throughout the many frameworks that have accreted to java. That said, I would like something that works kind of like this (let's call it package javax.stdio): Have a main utility class, perhaps FileStar, that can read and write files (or pipes), either text or binary, either sequentially or random access, with constructors that mimic fopen() and popen(). This class should have a load of useful methods that do things like fread(), fwrite(), fgets(), fputs(), fseek(), and whatever else (fprintf()?). Methods that are incompatible with the open/construct mode simply throw up (just like some of the collections classes/methods do when restricted). Then, have a bunch of interfaces that suggest how you intend to use the stream once you have created it: Sequential, RandomAccess, ReadOnly, WriteOnly, Text, Binary, plus combinations of these that make sense. Perhaps even have methods to return the appropriate type-cast (interface), throwing up if you have asked for something incompatible. For extra flavor, skip the declared exceptions -- e.g. - javax.stdio.IOException extends RuntimeException. Is there an open source project like this floating around?

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• Perl cron job stays running

  - by Dylan

  I'm currently using a cron job to have a Perl script that tells my Arduino to cycle my aquaponics system and all is well, except the Perl script doesn't die as intended. Here is my cron job: */15 * * * * /home/dburke/scripts/hal/bin/main.pl cycle And below is my Perl script: #!/usr/bin/perl -w # Sample Perl script to transmit number # to Arduino then listen for the Arduino # to echo it back use strict; use Device::SerialPort; use Switch; use Time::HiRes qw ( alarm ); $|++; # Set up the serial port # 19200, 81N on the USB ftdi driver my $device = '/dev/arduino0'; # Tomoc has to use a different tty for testing #$device = '/dev/ttyS0'; my $port = new Device::SerialPort ($device) or die('Unable to open connection to device');; $port->databits(8); $port->baudrate(19200); $port->parity("none"); $port->stopbits(1); my $lastChoice = ' '; my $pid = fork(); my $signalOut; my $args = shift(@ARGV); # Parent must wait for child to exit before exiting itself on CTRL+C $SIG{'INT'} = sub { waitpid($pid,0) if $pid != 0; exit(0); }; # What child process should do if($pid == 0) { # Poll to see if any data is coming in print "\nListening...\n\n"; while (1) { my $incmsg = $port->lookfor(9); # If we get data, then print it if ($incmsg) { print "\nFrom arduino: " . $incmsg . "\n\n"; } } } # What parent process should do else { if ($args eq "cycle") { my $stop = 0; sleep(1); $SIG{ALRM} = sub { print "Expecting plant bed to be full; please check.\n"; $signalOut = $port->write('2'); # Signal to set pin 3 low print "Sent cmd: 2\n"; $stop = 1; }; $signalOut = $port->write('1'); # Signal to arduino to set pin 3 High print "Sent cmd: 1\n"; print "Waiting for plant bed to fill...\n"; alarm (420); while ($stop == 0) { sleep(2); } die "Done."; } else { sleep(1); my $choice = ' '; print "Please pick an option you'd like to use:\n"; while(1) { print " [1] Cycle [2] Relay OFF [3] Relay ON [4] Config [$lastChoice]: "; chomp($choice = <STDIN>); switch ($choice) { case /1/ { $SIG{ALRM} = sub { print "Expecting plant bed to be full; please check.\n"; $signalOut = $port->write('2'); # Signal to set pin 3 low print "Sent cmd: 2\n"; }; $signalOut = $port->write('1'); # Signal to arduino to set pin 3 High print "Sent cmd: 1\n"; print "Waiting for plant bed to fill...\n"; alarm (420); $lastChoice = $choice; } case /2/ { $signalOut = $port->write('2'); # Signal to set pin 3 low print "Sent cmd: 2"; $lastChoice = $choice; } case /3/ { $signalOut = $port->write('1'); # Signal to arduino to set pin 3 High print "Sent cmd: 1"; $lastChoice = $choice; } case /4/ { print "There is no configuration available yet. Please stab the developer."; } else { print "Please select a valid option.\n\n"; } } } } } Why wouldn't it die from the statement die "Done.";? It runs fine from the command line and also interprets the 'cycle' argument fine. When it runs in cron it runs fine, however, the process never dies and while each process doesn't continue to cycle the system it does seem to be looping in some way due to the fact that it ups my system load very quickly. If you'd like more information, just ask. EDIT: I have changed to code to: #!/usr/bin/perl -w # Sample Perl script to transmit number # to Arduino then listen for the Arduino # to echo it back use strict; use Device::SerialPort; use Switch; use Time::HiRes qw ( alarm ); $|++; # Set up the serial port # 19200, 81N on the USB ftdi driver my $device = '/dev/arduino0'; # Tomoc has to use a different tty for testing #$device = '/dev/ttyS0'; my $port = new Device::SerialPort ($device) or die('Unable to open connection to device');; $port->databits(8); $port->baudrate(19200); $port->parity("none"); $port->stopbits(1); my $lastChoice = ' '; my $signalOut; my $args = shift(@ARGV); # Parent must wait for child to exit before exiting itself on CTRL+C if ($args eq "cycle") { open (LOG, '>>log.txt'); print LOG "Cycle started.\n"; my $stop = 0; sleep(2); $SIG{ALRM} = sub { print "Expecting plant bed to be full; please check.\n"; $signalOut = $port->write('2'); # Signal to set pin 3 low print "Sent cmd: 2\n"; $stop = 1; }; $signalOut = $port->write('1'); # Signal to arduino to set pin 3 High print "Sent cmd: 1\n"; print "Waiting for plant bed to fill...\n"; print LOG "Alarm is being set.\n"; alarm (420); print LOG "Alarm is set.\n"; while ($stop == 0) { print LOG "In while-sleep loop.\n"; sleep(2); } print LOG "The loop has been escaped.\n"; die "Done."; print LOG "No one should ever see this."; } else { my $pid = fork(); $SIG{'INT'} = sub { waitpid($pid,0) if $pid != 0; exit(0); }; # What child process should do if($pid == 0) { # Poll to see if any data is coming in print "\nListening...\n\n"; while (1) { my $incmsg = $port->lookfor(9); # If we get data, then print it if ($incmsg) { print "\nFrom arduino: " . $incmsg . "\n\n"; } } } # What parent process should do else { sleep(1); my $choice = ' '; print "Please pick an option you'd like to use:\n"; while(1) { print " [1] Cycle [2] Relay OFF [3] Relay ON [4] Config [$lastChoice]: "; chomp($choice = <STDIN>); switch ($choice) { case /1/ { $SIG{ALRM} = sub { print "Expecting plant bed to be full; please check.\n"; $signalOut = $port->write('2'); # Signal to set pin 3 low print "Sent cmd: 2\n"; }; $signalOut = $port->write('1'); # Signal to arduino to set pin 3 High print "Sent cmd: 1\n"; print "Waiting for plant bed to fill...\n"; alarm (420); $lastChoice = $choice; } case /2/ { $signalOut = $port->write('2'); # Signal to set pin 3 low print "Sent cmd: 2"; $lastChoice = $choice; } case /3/ { $signalOut = $port->write('1'); # Signal to arduino to set pin 3 High print "Sent cmd: 1"; $lastChoice = $choice; } case /4/ { print "There is no configuration available yet. Please stab the developer."; } else { print "Please select a valid option.\n\n"; } } } } }

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• How do I browse a Websphere MQ message without removing it?

  - by jmgant

  I'm writing a .NET Windows Forms application that will post a message to a Websphere MQ queue and then poll a different queue for a response. If a response is returned, the application will partially process the response in real time. But the response needs to stay in the queue so that a daily batch job, which also reads from the response queue, can do the rest of the processing. I've gotten as far as reading the message. What I haven't been able to figure out is how to read it without removing it. Here's what I've got so far. I'm an MQ newbie, so any suggestions will be appreciated. And feel free to respond in C#. Public Function GetMessage(ByVal msgID As String) As MQMessage Dim q = ConnectToResponseQueue() Dim msg As New MQMessage() Dim getOpts As New MQGetMessageOptions() Dim runThru = Now.AddMilliseconds(CInt(ConfigurationManager.AppSettings("responseTimeoutMS"))) System.Threading.Thread.Sleep(1000) 'Wait for one second before checking for the first response' While True Try q.Get(msg, getOpts) Return msg Catch ex As MQException When ex.Reason = MQC.MQRC_NO_MSG_AVAILABLE If Now > runThru Then Throw ex System.Threading.Thread.Sleep(3000) Finally q.Close() End Try End While Return Nothing 'Should never reach here' End Function NOTE: I haven't verified that my code actually removes the message. But that's how I understand MQ to work, and that appears to be what's happening. Please correct me if that's not the default behavior.

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• problems doing the Django tutorial on Dreamhost using Passengers

  - by Pietro Speroni

  I have looked and I could not find this question before, and it surprises me. I am reasonably proficient in Python, and I used Dreamhost for a number of years. Now I would like to learn Django. They are finally supporting it using Passenger. Which I do not know what is. Following the instructions on Dreamhost I installed Django. Then I started following the tutorial 01. This went well, except that I could not start the server (this in the tutorial) since the code was live on dreamhost. At the time this did not seem to make any difference. Then when I went on the second part of the tutorial I had to access the admin site. And it worked well going to myurl/admin/ , as it should. But here the problems started. According to the tutorial (here) I have to add a file in the poll application and then restart the server. But I never started the server in the first place, my code is running live on the web... but when I add a file the website the admin acts as if it does not see it. Probably dreamhost has started its own server, and I don't know how to restart it. But I assume this is going to be a common problem when you run django on dreamhost. Every time you add a file you will have to tell the server to consider it. So what should I do to let the server know about it? Thanks, Pietro

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• Special technology needed for browser based chat?

  - by orokusaki

  On this post, I read about the usage of XMPP. Is this sort of thing necessary, and more importantly, my main question expanded: Can a chat server and client be built efficiently using only standard HTTP and browser technologies (such as PHP and JS, or RoR and JS, etc)? Or, is it best to stick with old protocols like XMPP find a way to integrate them with my application? I looked into CampFire via LiveHTTPHeaders and Firebug for about 5 minutes, and it appears to use Ajax to send a request which is never answered until another chat happens. Is this just CampFire opening a new thread on the server to listen for an update and then returning a response to the request when the thread hears an update? I noticed that they're requesting on a specific port (8043 if memory serves me) which makes me think that they're doing something more complex than just what I mentioned. Also, the URL requested started with /tcp/ which I found interesting. Note: I don't expect to ever have more than 150 users live-chatting in all the rooms combined at the same time. I understand that if I was building a hosted pay for chat service like CampFire with thousands of concurrent users, it would behoove me to invest time in researching special technologies vs trying to reinvent the wheel in a simple way in my app. Also, if you're going to do it with server polling, how often would you personally poll to maximize response without slamming the server?

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